Comparison shopping: detectability and mate preferences in a fiddler crab

Females commonly exhibit mating preferences when they are allowed to choose between two alternative courtship signals. However, they also commonly approach any courtship signal when presented on its own (no-choice experiments). This could have consequences for male and female fitness. Males with nonpreferred stimuli may successfully attract females if they are, fortuitously, far enough away from competing males to prevent direct comparison. In the banana fiddler crab, Uca mjoebergi, we show, using a combination of no-choice and two-choice experiments, that there was interplay between detectability and preference. We found that preferred stimuli were not more detectable at a distance. Females were more likely to exhibit a preference when they could directly compare two stimuli that were close together and viewed in the same field of vision. Once the decision to approach one male over another had been made, it was not changed, even when more information became available.